Mayor Bloomberg, joining forces with frequent adversary Assembly Speaker Sheldon Silver, has launched a campaign against the Port Authority in an attempt to force the agency to agree to put up more money at the World Trade Center.

Officials from the city and the bistate Port Authority have been engaged in intense talks as they try to back financing for two office towers at the site, which would be built and owned by private developer Larry Silverstein. The towers have no private tenants, though Mr. Silverstein insists the public sector has a moral and legal responsibility to let him build given its own delays at the site—a point that surely would be debated in court if it goes that far.

Mr. Bloomberg on Wednesday attacked the Port Authority in a statement issued with Mr. Silver, who has previously opposed the mayor on numerous economic development projects including aspects of the World Trade Center debate. This marks the second high-profile issue that the two foes have recently agreed upon—Mr. Silver supported a modified version of mayoral control of the city schools, a pet initiative of Mr. Bloomberg.

On Wednesday, speaking to reporters, Mr. Bloomberg kept up the pointed criticism.

“What’s good for America and good for New York City may be slightly at odds with what’s good for the Port Authority,” he said. “We cannot leave a hole in the ground and the Port Authority just has to come to the party.”

“This is not one party against another,” Bloomberg said at the time. “No matter how anybody tries to pull us apart and get one side to trade against another, we’re not going to fall for that bait. That’s gone on for much too long.”

It is notable that Mr. Bloomberg did not direct his criticism directly at the governors of New York and New Jersey, who control the Port Authority. Rather, it was directed at the agency as an entity itself, perhaps in an effort to isolate it from the governors. After all, he wants Governors Corzine and Paterson to eventually direct the agency to back well over $2 billion in additional financing; agency officials have strenuously resisted financing two towers, saying the money would come at the cost of essential transportation projects.

The approach also reflects a change in alliances. In the last renegotiation at the site, Mr. Bloomberg fought Mr. Silverstein and partnered with New Jersey officials at the Port Authority. Mr. Silver has long been one of the more supportive players toward Mr. Silverstein downtown.